A semiconductor device like that shown in FIG. 1 has been proposed as a memory using a TFT whose active layer is made of amorphous oxide. The semiconductor device includes a first transistor 20 and a second transistor 21. The first transistor is formed over a substrate containing a semiconductor material. The second transistor includes an oxide semiconductor film. In addition, Patent Document 1 discloses a ROM circuit using a TFT whose active layer is made of amorphous oxide.